The current list of alterations isn't by any means a comprehensive list of all possible abilities for a grim. New alterations may be added. Here are some tips to help maintain the spirit of design for alterations.

Avoid effects that directly emulate spells: While an alteration may include spell-like effects, it shouldn't simply grant use of a spell. That's what the spell is for. If you wish to add an ability that allows the grim to use a spell that isn't on his spell list, consider instead a grim feat, as there are several that expand the grim spell list. Alterations may grant variant versions or modified versions of spell effects however, playing to the strength of what alterations allow, unique abilities. In addition, while a grim casts spells divinely, he does gain access to many spells that are typically arcane.

Avoid effects that are available as feats: An alteration shouldn't be a means of gaining the effect of a feat without needing to gain a feat. That's what the feat is for. As alterations are gained with higher frequency, emulating feats is potentially unbalancing. Many alterations are feat-like, with passive bonuses that can be later attained as continually functioning, with Imbued Body. However, these passive abilities are supernatural, unlike most feats, which are a measure of training or manifestation of in-born powers. Alterations stem from the grim's connection to another plane of existence and his ability to channel that power.

Prerequisites should be limited to other alterations and skill ranks: This is for the sake of establishing standards, as well as easily recognizable points of when the ability can be gained. There are exceptions, first being Epic. The second being progressing off of a grim feat specifically. As a prerequisite, access to grim class features is to be avoided, opting instead for skill ranks. Skill ranks are not to be confused with skill modifiers, as ranks are only gained through leveling and using skill points.

All prerequisites are to be listed for each alteration: This means to include those prerequisites which are for other alterations in its progression. Elemental Burst is an example of this, listing its prerequisite alteration as well as the prerequisites for that alteration (and so on) as well.

Consider how a new alteration interacts with existing alterations as well as spells, feats and other abilities: When adding a new alteration, be sure to consider the big picture of the game that it will be entering. Loopholes and problems can pop up quickly if research is ignored. Research is important in designing any game mechanic.

Consider why this alteration doesn't yet exist: An alteration may not exist because no one thought of it and added it or the alteration was thought of, and purposely not added. Some effects and abilities may seem like they fit well with the class or one of its variants, but be sure to make this consideration anyways. The more thought put into designing your new alteration, the better the result will be.

Keep it simple: Mechanics should be easy to remember, using standards whenever possible, and using a minimum of rolls and numbers to keep track of. Alterations shouldn't slow the game down.

Aura is centered on the grim: Aura alterations are always centered on the grim and are either spherical bursts, passive auras or simply affect adjacent targets (or those within the grim's space). Auras may be passive, if the effect is constantly granted just by having the alteration.

Bursts are short "explosions": Burst alterations require an action to use, typically a standard action. Aura bursts are centered on the grim. Bursts may be centered on other things as well, and function much like fireball (but with less fire, typically).

Passive alterations always function: Once you transform, a passive alteration begins functioning, granting its ability. If the alteration has another purpose, it also gains the Special type. Be sure when designing passive alterations to consider the effects of Imbued Body, as having the alteration function continuously can dramatically change the power of the grim. Passive abilities are to be aimed in power to around that of a normal ability boost gained at its earliest entry level (similar to that of a feat, but different in design philosophy and function) for purposes of balance. Passive alterations, like feats, may represent a gain in power through training or racial effects, as well as other unusual powers manifested from his planar connection.

Special alterations are the oddballs: These alterations require some sort of action to use, often a standard action or swift action. They have various effects, and might create cone-shaped bursts, grant unusual powers, or some other boon.

Entry level alterations are "weaker" than ones with prerequisites: While alterations should be designed to allow useful function at all levels of the game, entry level alterations are often weaker, since they can be gained as soon as 2nd level. Just like low-level spells, some alterations outlive their functionality. However, most entry level alterations are stepping stones to more powerful versions of the ability. Vigorous Healing may only grant fast healing 1, but its the first step in more powerful abilities.

Alterations are built to the power of the earliest level they can be obtained at: This is the main reason there is no ability that grants bonus alterations. The system is balanced to allow more powerful abilities at higher level, with appropriate numbers of prerequisites to ensure that certain abilities can only be gained at certain levels. Feats and alterations are not interchangeable for power.

Alterations have a standard wording: Passive alterations should start with "While transformed, you...". Other alterations should begin ""As a standard action while transformed, you...".

Quotes are often 3rd person perspective: Quotes for alterations somehow became more like short snippets of stories, a sentence or two long, often without resolution to the action at hand. This is meant to empower the reader to employ his imagination into the scenario, adding possibilities of how the ability could be used. Though, quotes may be done in any manner, they should reflect some usage and description of the ability. The purpose of the quote is to provide extra information for using the ability in the game and adding flavor without interfering with the mechanical description of the alteration.

Formatting is important: Alterations should be well formatted as well as worded. A clean, easy to read ability with appropriate links and capitalized words (the specific names of alterations are capitalized, such as Wings, just like feats).

Names should be interesting but not confusing: Naming alterations can be a bit of a pain. A name should be both descriptive as well as easy to understand. In addition, it should allow the player, if he is required to actively us it to say something like "I use my Fill-in-the-blank..." and not stumble over it. Additionally, names should never have commas. Names that appear in the table as prerequisites and have commas cause confusion (as all alterations are separated by commas).

Ask around, get advise: Designing any game mechanic gets easier with the input of other people who know what they are talking about and can help you brainstorm ideas or look things over to see if you missed anything. Sometimes, what you thought was clear, wasn't translated so well to words.